Compositions comprising transition metals for treating and monitoring liquid systems

ABSTRACT

Methods for utilizing transition metals as tracers in aqueous liquid systems are provided by this invention. Transition metals with low background levels in system waters are identified as preferred when soluble in said aqueous liquid systems. The transition metals show low levels of deposition on equipment scale and provide reliable information as to the process history of the liquid systems.

This is a division of application Ser. No. 315,713, filed Feb. 27, 1989,now U.S. Pat. No. 4,966,771.

FIELD OF THE INVENTION

The present invention pertains to the utilization of transition metalsas tracers to quantify the change in the level of treatment chemicalsunder static and changing operating conditions of liquid systems and tocontrol feed rates of treatment chemicals into liquid systems. Further,transition metal concentration can be used to quantify importantcharacteristics of the system such as total volume and amount of aliquid entering and/or leaving the liquid system.

BACKGROUND OF THE INVENTION

In a system involving a body of liquid to which a treating agent isadded, maintaining the proper feed level for the agent is essential foroptimal performance. An improper feed rate of treating agent can lead toserious problems. For example, severe corrosion and deposit formationcan rapidly occur on heat-exchanger surfaces in cooling water systemswhen incorrect levels of treating agent are used. One common method ofestimating the concentration of a treating agent focuses on measuringthe level of an active component in the treatment formulation (e.g.,polymeric scale inhibitor, phosphate, or organophosphate). Thattechnique is often unsatisfactory due to one or more of the followingproblems:

background interferences from the system liquid or materials containedin the liquid;

analytical methods require bulky and costly equipment;

time-consuming, labor-intensive analyses are not compatible withcontinuous monitoring; and

inaccurate readings result from degradation or deposition of activecomponent within the system.

An alternative method of determining treatment feed rates is to addtracer compounds to the formulation or system. This method helpscircumvent the degradation, deposition, and background interferenceproblems that commonly occur when measuring the level of an activecomponent in a treatment formulation. However, quantitation of lowtracer levels commonly magnifies problems associated with expensiveequipment and time-consuming test methods. Additional factors which mustbe considered are cost and environmental acceptability of the tracer.For example, radioactive tracers are detectable at very low levels, butare generally expensive and unacceptable due to environmental and healthconcerns.

Ultimately, compounds selected as tags or tracers serve as indices toother chemicals present in an aqueous system. These tags or tracers areselected to fulfill certain criteria. For example, certain tracers aredetectable by electronic devices on a continuous or semi-continuousbasis. In addition, certain tracers provide measurements ofconcentration that are accurate, repeatable and/or capable of beingperformed on many different waters (i.e., clean, turbid, hard, soft,etc.) and variations of these waters. To achieve these goals, the tracerselected is preferably not present in significant quantities within thewaters tested. In addition, the tracers selected must be quantifiable bytests that are not interfered with or biased by other chemical compoundsnormally present in the water to be tested. The tracers selected arepreferably inert and stable in the treatment water and do not reduce theactivity of the treatment chemicals themselves.

The tracers must be soluble in the waters to be tested and must becompatible with the treatment chemicals with respect to formation,storage, freeze-thaw recovery, etc. Most importantly, the tracers mustshow a minimal incorporation into the equipment scale as compared to thetreatment chemicals. Incorporation is the transfer of tracer from thetreated aqueous system to the surfaces of the system. equipment. Last,the tracers should not present any sort of environmental problems in theevent of discharge. To avoid costly disposal methods, it is preferablefor the tracer to be functional at levels sufficiently low so thatdischarge does not pose a health concern. The tracer is preferablynon-toxic at high concentrations. The tracer must be sufficiently safeso that its use at the concentrations desired conforms to allgovernmental regulations.

Chromium VI (e.g. bichromate, Cr₂ O₇ ⁻²) has been used as a tracer incooling waters in industrial cooling water systems. However, theEnvironmental Protection Agency and Occupational Safety HazardAdministration have restricted the use of Chromium VI in industry. Alsochromium (VI) is a reactive, oxidizing agent and alternative tracercompounds are needed.

The present invention is based on the discovery of a new class of tracercompounds that meet the above specified criteria.

SUMMARY OF THE INVENTION

It has been discovered that transition metals, as a class, will satisfythe criteria for use as tracers if they are soluble in the liquid mediumto be tested. The transition metals have been found to exhibit minimalincorporation into equipment scale and typically exhibit much lowerincorporation than the treatment chemicals used in the liquid systems.Measuring the concentration of the transition metals provides moreaccurate information as to the volume of liquid and the amount oftreatment agent added to the liquid system. As a consequence, thisinvention provides methods for using transition metals as tracers andcompositions containing transition metal tracers therein.

The transition metals have been found to perform better as tracers thansome non-transition metals because their rate of incorporation intodeposits in the system is much lower. The most preferred embodiments ofthis invention employ transition metals which show lower incorporationinto deposits in the system than Chromium VI, such as vanadium.

Natural sources of makeup waters have been found to have very lowconcentrations of transition metals as compared to non-transitionmetals. For example, aluminum and sodium are non-transition metals whichhave been found to be present at high background levels in many makeupwaters. Preferred embodiments of this invention are directed to thosetransition metals identified as having low background levels in themakeup waters of most industrial cooling water system, permitting lowerconcentrations to be used.

The transition metals Chromium VI and lead are excluded from those usedin the present invention because their use is limited by governmentalagencies.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1--Is a schematic representation of a cooling water system, morespecifically, a pilot cooling tower.

FIG. 2--Is a representation of the effective concentration ofrecirculating water over time.

FIG. 3--Is a representation of the effect of adding tracers to largevolumes of liquid wherein the effective volume is much smaller than thetrue volume.

FIG. 4--Is a graph of the chemical treatment concentrationdeterminations on vanadate tracer and bichromate (Cr₂ O₇ ⁻², wherechromium is formally +6 oxidation state) tracer in a pilot coolingtower.

DETAILED DESCRIPTION OF THE INVENTION

It is an object of the present invention to avoid all of theaforementioned problems by incorporating a transition metal compound asa tracer into a treatment formulation for industrial process waters toprovide lo quantitative measurement and control of treatment chemicalfeed rate and performance.

The phrase "transition metal compound" as used herein is intended toinclude transition metal ions, oxyanions, cations and associatedcomplexes which are soluble in water. This phrase is also intended toinclude those compounds which form these ions, cations, oxyanions andcomplexes in water. The water soluble species are especially suitablefor quantitative measure. This measurement allows for the calculatedcontrol of the feed rate of water and water treatment chemicals in fluidsystems such as industrial process waters.

Most industrial operations utilize some aqueous systems which must betreated before being transferred to the environment; recycled to thesystem or process; or fed to the system or process. Preferably, aqueoussystems are contemplated by this invention which include, but are notlimited to, domestic wastewater, process wastewater, cooling watersystems, boiler water or any other aqueous system that is treatedphysically or chemically before use in a process, during use in aprocess or before discharge to the environment where it is necessary toquantify the effects of the physical or the chemical treatment. Thisinvention can also be utilized in a broad range of aqueous, mixedaqueous/non-aqueous, or non-aqueous liquid systems where the level ofphysical or chemical treatment affects performance of the system.

The most preferred aqueous system contemplated by this inventioninvolves the treatment of cooling waters used in cooling systems.Cooling systems used in industrial processes typically include multiplewater flow pathways through heat-exchangers, multiple sources of"makeup" and "blowdown" water, and control means for maintaining desiredprocess conditions. Desired process conditions may include properchemical treatment concentrations, temperature, water flow rate, waterquality, and pH. A simplified version of an industrial cooling watersystem is a pilot cooling tower (PCT) shown in FIG. 1.

In pilot cooling towers, energy is extracted by the recirculatingcooling water from the process-side of the system which is at a highertemperature by a heat exchanger (5). To maintain the efficiency of thatheat transfer, energy is removed by evaporative cooling of therecirculating water in the cooling tower (10). Evaporation (E) of thecooling water leads to concentration of the suspended and dissolvedsolids in the cooled water (15). The concentration ratio (CR) is ameasure of the increased level of dissolved and suspended matter in asystem (eq 1), where CR≧1.0. ##EQU1##

The heat-exchanger surfaces need to remain clean to maintain efficiency.Deposition of solids and corrosion of heat-exchanger surfaces areproblems most generally encountered. Cooling water systems commonlycontain highly supersaturated levels of scaling salts. Deposition ofsolids throughout the system (particularly at metal heat-exchangers)will occur unless one or more chemical treatments (CT) such as scaleinhibitors are added from source (25). To prevent corrosion of metalheat-exchangers and water transfer lines, chemical treatments commonlycontain corrosion inhibitors. If the feed rate of the chemical treatmentis too high or too low, severe scaling and corrosion can occur on theheat-exchangers and throughout the system.

It is vital that the level of dissolved and suspended solids, totalvolume of system's liquid and concentration of chemical treatment bemaintained between certain values in order to provide economical usageof water, efficient heat transfer, minimal fouling of entire coolingsystem, and low operating costs. To maintain the concentration ratio(CR) within an acceptable range, water containing a "high" concentrationof impurities must be removed from the system, collectively defined as"blowdown" (B), and replaced by water containing a "low" concentrationof impurities, collectively defined as "makeup" (M). The value forconcentration ratio, evaporation, blowdown and makeup water are variabledue to changes in the weather, operating conditions of the industrialplant, and quality of the makeup water. Those factors are allinterrelated and a change in any one of those factors must becounterbalanced by corresponding changes in other operating parameters.

In addition to the dynamic operating conditions of a cooling watersystem, other significant variables and unknown factors are commonlyencountered. For example, blowdown water (B) can be removed from thecooling system through a variety of ways, some of which tend to beill-defined in nature. The rate at which water is specifically pumpedfrom the cooling water system is defined as "controlled water blowdown".Controlled water blowdown is not always accurately known due topractical difficulties in measuring large volumes of water. In addition,ill-defined amounts of recirculating water (un-accounted system losses)are commonly removed from the cooling water system to be used in otherareas of the industrial plant, defined as "uncontrolled plant blowdown".Leakage of recirculating water and drift of liquid droplets from coolingtowers also add to unaccounted system losses. A similar situation canoccur with the makeup water, where the total makeup water rate (M) isthe combined rate at which makeup water is specifically pumped into therecirculating system and liquid originating from other sources. The feedrate of chemical treatment into the cooling water system is commonlybased on estimated values for recirculating water blowdown and makeupwater pumped into the recirculating system which means there can beconsiderable uncertainty regarding the concentration of the chemicaltreatment. When operating conditions of the cooling water system change,the feed rate of the chemical treatment should be adjusted. Thoseadjustments may or may not be made, depending on how carefully thecooling water system is monitored and controlled. Even when feed ratesare adjusted, the concentration of chemical treatment within a coolingwater system generally may respond slowly to the change.

For example, where a system containing one million gallons has a totalblowdown rate of 300 gal/min and the treatment feed rate is increasedfrom 50 to 100 ppm, about 38.5 hours are required for only half of thatchange (25 ppm increase in treatment concentration) to be attained,assuming that no other fluctuations or changes have occurred within thesystem. For very large volumes and small values of blowdown, responsetime may be measured in days or weeks. In other cases, changes can occurrapidly, such as purposeful (or inadvertent) flushing of the system.Therefore, it is important that good control and accurate monitoring ofthe system be maintained.

Another significant operating parameter which should be quantified isholding time index (HTI), a measurement of the half-life .of a chemicalspecies within the system.

Under severe operating conditions, it is important to optimize HTI inorder to reduce possible degradation of components in the chemicaltreatment without greatly increasing operating costs.

Due to all the operating limitations and uncertainties in cooling watersystems, the need to rapidly determine and continuously monitor theconcentration of chemical treatments is clearcut. The addition of atracer to the chemical treatment permits accurate determination of allthe known, imprecisely known, and variable operating conditions or"parameters" which vary with the composition of the liquid system, suchas the present volume of a liquid system, the changes in volume of sucha system, the quantity of treatment agent added to the system, thechanges in the concentration of the treating agent and the lifetime ofthe treating agent within the system.

Transition metal compounds have been found which are soluble in aqueoussystems as ions, oxyions, cations or associated complexes. Transitionmetal compounds have been found to be low in background presence withinthe makeup waters for substantially all industrial cooling towers,making their use as tracers very economical and efficient.

A survey of the system waters used in recirculating industrial coolingwater systems suggests that the background presence of transition metalcompounds within these waters is generally less than ppm. The backgroundlevels of most transition metal compounds within at least 80% of thesystem waters tested was found to be below 0.1 ppm. There have been someexceptions, such as zinc and iron; however, as a class, transitionmetals have been found to have a lower background presence in thesewaters than other metals such as aluminum, lithium, boron and strontium.

The preferred class of transition metal compounds include those whichare soluble in aqueous liquid systems and show background levels of lessthan 0.01 ppm within 80% of the waters tested. These preferredtransition metal compounds include those of cobalt, vanadium, titaniumand yttrium.

Other members of the preferred class include those which show backgroundlevels of less than 0.1 ppm in 95% of the waters tested. These includethose transition metal ions mentioned above, plus nickel, molybdenum(molybdate), and tungsten (tungstates). It is important that the tracerhave low background presence within the makeup waters so as to limit theamount necessary to be added to function effectively as a tracer. It ispreferable that the background level of a tracer provide no more than 1?% of the signal which quantifies the level of transition metal in asample.

Other transition metal compounds evaluated for use as tracers by thisinvention include those of copper, Chromium III and manganese. Ions ofthese transition metals are present as background in cooling watersystems typically at relatively higher levels than the above mentionedtransition metals, requiring higher levels to be added to the aqueoussystem and making them less cost effective.

Certain transition metals are well recognized as toxic at low levels andsome have raised questions as to whether they pose health hazards tohumans, i.e., carcinogens, mutagens, etc. For example, lead has longbeen recognized as toxic at very low levels and its use in gasoline hasbeen restricted. Other species which raise health questions includecadmium and mercury. Each transition metal chosen (and the amount used)must conform to governmental guidelines. The use of Chromium VI hasrecently been regulated by the EPA and other governmental agencies.Consequently, lead, cadmium, mercury and Chromium VI are not consideredsuitable for use in this invention.

Other transition metal compounds are contemplated for use in the presentinvention; however, they are not preferred in that they are eitherpresent at high background levels in the makeup water for cooling watersystems, or show poor solubility in aqueous liquid-systems. Examples oftransition metal compounds which are excluded because they are insolublein aqueous systems, or show very low solubility include those ofzirconium and silver.

The transition metal compound chosen for any particular system must besoluble in the system, i.e. it must be ionized or dissociate to solubleions, cations, etc. Additionally, the transition metal compound tracershould be chosen within those permitted by governmental guidelines. Forexample, OSHA and the EPA have restricted the use of Chromium VI inindustry to the extent that its use as a tracer cannot be tolerated inall instances. In selecting a transition metal compound for use in areducing environment, it may be desirable to choose metal ions which arein their lowest oxidation state or are weak oxidizing agents or arekinetically-stabilized towards reduction so that the metal tracer ionswill not be reduced in their application. This conversion may interferewith the detection of such transition metals. For example, Cr⁺⁶ canreadily be reduced to Cr⁺³, and may go undetected as Cr⁺³ in subsequentquantification tests. On the other hand, Vanadium (V⁺⁵), also referredto herein as Vanadium V, is a weak oxidizing agent in cooling waterapplications and tends to resist reduction to lower oxidation stateswhich would not be detected by the analysis method. In addition, higheroxidation states beyond Vanadium V are not known so there is no concernwith V⁺⁵ tracers being converted to higher oxidation states which wouldnot be detected by the analysis method. Since Vanadium V is already inits highest oxidation state there is no concern that it will beoxidized.

Soluble transition metal compounds are effectively used as cooling watertreatment chemical tracers to allow the easy and accurate determinationof chemical feed rates. These transition metal tracers may be added tothe aqueous system directly but are preferably added to a treatmentformulation such as a scale inhibitor or corrosion inhibitor. Theaddition of tracer compounds to liquid systems is very useful as adiagnostic tool for quantifying system characteristics and identifyingand quantifying problems within the system. Also, the addition of atracer to treatment formulations is very useful for measuring treatmentconcentration and efficacy.

Transition metal compounds offer a number of advantages as tracers.Nearly all transition metal compounds have negligible background levelsin makeup waters so that interference is minimal. Many are not healthhazards due to their low toxicity at the very low levels needed tofunction as tracers in most cooling systems. Additionally, mosttransition metal compounds when in the form of ions, cations, associatedcomplexes, etc. are sufficiently inert, stable and soluble in a coolingwater environment. The transition metal compounds are typically morestable than the treating agents which they "trace".

By means of a sensitive analytical method, preferably colorimetric, thetransition metal compound concentration measured is used to determinethe level of treating agents. Other possible methods of detectingtransition metal concentration include ion selective electrodes,fluorometric analysis and voltametric analysis, as well as otherconventional techniques for detecting ions.

As noted above, the preferred method of detecting transition metals is acolorimetric method. Colorimetry refers to the determination of asubstance from its ability to absorb visible light. Visual colorimetricmethods are based on a comparison of a blank or known solution withknown concentration with that of a sample of unknown concentration. Inspectrophotometric methods, the ratio of the intensities of the incidentand the transmitted beams of light are measured at a specifiedwavelength by means of a detector such as a photocell or photomultipliertube.

Molecular absorption in the ultraviolet and visible region depends onthe electronic structure of the molecule. The energy absorbed elevateselectrons from orbitals in a lower-energy state to orbitals in ahigher-energy state. Since only certain states are possible in anymolecule and the energy difference between any ground and excited statemust be equal to the energy added, only certain frequencies can beabsorbed. When a frequency that is absorbed by the molecule is found,the intensity of the incident energy is greater than the intensity ofthe emergent energy. Radiant power is defined as the radiant energyimpinging on unit area in unit time. Transmittance is defined as theradiant power after the energy has passed through the absorbing solutionand cell wall divided by the radiant power of the incident beam, [referto Bauer, Christian and O'Reilly; "Instrument Analysis" (1978)].

Typically, in measuring the transmittance of a sample, a blank is madethat contains all the reagents in solution except the compound ofinterest. Then, the measuring device is set at 100% for the blank.Thereafter, any reading of an actual sample will be the true absorbanceminus any effects due to the holding cell or the reagent solution. Theintensity of radiation absorbed in a thin layer of material depends onthe absorbing substance and on the frequency of the incident radiation,and is proportional to the thickness of the layer. At a givenconcentration of the absorbing substance, summation over a series ofthin layers, or integration over a finite thickness, lead to anexponential relationship between transmitted intensity and thickness.According to Beer's law, the amount of radiation absorbed or transmittedby a solution or medium is an exponential function of the concentrationof absorbing substance present and of the length of the path of theradiation through the sample. Therefore, a plot of the absorbance, whichis equal -log(%T/100), versus concentration should give a straight linepassing through the origin. When known concentrations of a compound aremeasured, a calibration curve, or in this case, a straight line, of theknown concentration versus absorbance may be plotted. Finally, thesamples with unknown concentration may be compared to the calibrationcurve to determine its concentration.

In the visible and ultraviolet regions, spectrophotometric methods maybe used for the quantitative determination of many trace substances,especially inorganic elements. The basic principle of quantitativeabsorption spectroscopy lies in comparing the extent of absorption of asample solution with that of a set of standards under radiation at aselected wavelength.

In many instances, the sample compound does not absorb radiationappreciably in the wavelength regions provided or the absorption is slow that it is desirable to form a light-absorbing tracer or at leastbetter light-absorbing substance by reacting the compound in questionwith other reagents. The reagents should be selective in their reactionsand should not form interfering absorbing species with foreignsubstances likely to be present.

Some of the factors that should be considered when forminglight-absorbing compounds from tracer ions include: pH, reagentconcentration, time, temperature, order of mixing reagents, stability,available masking agents, organic solvent, and salt concentration.

The pH plays a very important role in complex formation. Adjustment ofpH or the use of a buffer often eliminates certain interferingreactions. Additionally, some transition metals are insoluble at high pHlevels. One such metal is cobalt but it can be resolubilized by loweringthe pH.

The amount of reagent required is dictated by the composition of theabsorbing complex formed. An optimum concentration of reagents should bedetermined, since either not enough reagent or too much reagent cancause deviation from Beer's Law. Formation of the absorbing complex maybe slow or fast with color development times ranging from severalseconds to several hours. Therefore, in processes where time is of theessence, a complexing reagent that reacts quickly is important.Additionally, reaction rates are often affected by temperature. Certainreactions require elevated temperature to decrease the time necessaryfor complete color development.

Frequently, it is important to add the reagents in a specified sequence,otherwise full color development will not be possible or interferingreactions may occur. For instance, the highly selective color reactionof cobaltic nitrilotriacetate in the presence of hydrogen peroxide mustbe preceded by the formation of the cobaltous nitrilotriacetate complex.If the absorbing complex formed is not very stable, the absorbancemeasurement should be made as soon as possible. If the absorbing complexis photo-sensitive, precautions should be taken in order to avoid itsphotodecomposition.

The presence of masking agents is often necessary to prevent complexingof other reagents. For example, in the presence of excess EDTA, ferricion does not form the colored FeSCN²⁺ complex with a thiocyanate ion.Many organic reagents or complexes are only slightly soluble in water.In such cases, it is necessary to add immiscible organic solvent toavoid precipitation or to aid color development. Finally, it should berecognized that high concentrations of electrolyte often influence theabsorption spectrum of a compound.

Transition metal compound concentrations when added to an aqueous systemas tracers, can vary from parts per trillion (ppt) to parts per million(ppm). Detection of these compounds can be routinely accomplished on aninstant or continuous basis with inexpensive portable equipment. Inaddition, multiple tracers may be used concurrently by choice oftransition metal compounds with proper spectral characteristics or othertracers. As such, various combinations of transition metals andtreatment feeds can be quantified within a liquid system. For example,several individual treatments containing different transition metalcompounds can be employed within a liquid system. In that case, eachtransition metal compound and the corresponding individual concentrationof each of the treatments can each be quantified. In addition to beingable to quantify complex combinations of the treatment feeds, transitionmetal compounds are available which are environmentally acceptable, arenot degraded by or deposited within the liquid systems, and are low incost.

The invention can generally be applied in the following ways:

(a) direct addition of from one or more transition metal compounds withor without other conventional tracers to a liquid system;

(b) incorporation of 1 to 6 (or even more) transition metal compoundsinto chemical treatment compositions containing other components whereinsaid treatment is applied to liquid system in order to maintain properoperation of that system;

(c) addition of 1 to 6 chemical treatment agents (or even more)containing transition metal compounds directly into liquid system orinto liquid feed leading into system; and

(d) addition of transition metal compounds without treatment agents sothat within the liquid system individual tracer concentrations rangingfrom 1 part per trillion (ppt) to 100 parts per million (ppm),preferably from 1 preferably from 10 ppb to 2 ppm are realized.

FIGS. 2A-C demonstrate the operation of the water treatment program atthe molecular level as a function of time. In FIG. 2A, the concentrationof chemical treatment (CT) contains phosphorus (P'), polymer (P) andtracer (T). This chemical treatment is slowly fed via feedline into therecirculating cooling water where the treatment is rapidly diluted anddistributed throughout the system. If operating conditions of thecooling water system remained constant, the addition and removal oftreatment due to recirculating water blowdown (B) would equilibrate. Theconcentration of the chemical treatment and its components ideallyshould remain unchanged. However, that situation never occurs. As timeprogresses (FIGS. 2B-C), additional amounts of polymer, andphosphorus-containing compounds can be lost from the recirculating water.due to deposition and protective-film formation on metal surfaces andchemical/biological degradation processes. Also, changes in operatingconditions (blowdown rate, concentration ratio, and product feed rate,and others) affects the concentration of the treatment components.Without a tracer, analysis of the recirculating water may measurecurrent concentrations of some of the treatment components (assuming ananalysis method exists), but cannot directly indicate the original feedrate of the treatment program. Use of a tracer to quantify and controlthe treatment feed rate is a valuable addition to current watertreatment programs.

FIGS. 2A-C also indicate how addition of an inert tracer can provideaccurate determination of treatment feed rate and treatment efficacy, inspite of deposition of other components in the chemical treatment. Forexample, assume the formulation feed rate was 100 ppm. If depositionoccurred on the heat-exchangers, 40% of the phosphorus-containingspecies could be lost from the recirculating water, but little or noneof the transition metal tracer will be lost. The total phosphorusconcentration would suggest only 60 ppm of the product was present.However, the transition metal ion tracer would more closely indicate theformulation feed rate of 100 ppm and a loss of phosphorus-containingcomponents equivalent to that supplied by 40 ppm feed of formulation wasbeing deposited. Determination of loss rates of active component(s) ofthe treatment is a direct measurement of treatment efficacy.

One method of evaluating transition metal compounds as tracercompositions is to compare their measured deposit enrichment ratio (DER)(eq 2) against the DER values for the active components. ##EQU2##Preferably, the DER value of the tracer is lower than that of active andreadily analyzed components of the treatment formulation. The lower theDER values under scale forming conditions the better. While low DERvalues are desired, the tracer compound should also exhibit goodstability and not decompose when in use. For example, it is known thatvanadium responds to pH changes more favorably than Chromium VI as shownin FIG. 4.

Important system characteristics of many industrial systems (totalvolume, blowdown, and makeup rates, holding time index, treatment feedrates and others) are imprecisely known, variable and sometimesunpredictable in nature. Lack of knowledge regarding those factors canlead to serious deposit and corrosion problems throughout the entirecooling water system. In particular, over/underfeeding of treatmentprogram or improper operation of cooling water system can result insignificant loss of treatment component(s) and adversely affect heattransfer within a cooling water system. In addition, water treatmentprograms commonly contain regulated or toxic materials (e.g. phosphateor chromate). Overfeeding of treatments can be hazardous and makes itmore difficult for industrial sites to meet governmental restrictions oneffluent discharges. Use of the transition metal tracers identifiedherein is a highly desirable means of accurately determining,continuously monitoring, and controlling cooling water systemcharacteristics and treatment feed rates within desirable ranges.

Preferably, transition metals are used as chemical feed tracers inindustrial cooling water systems. However, there are numerous examplesof industrial systems whereby a chemical treatment is added to a movingliquid in a containment structure(s) and associated transfer lines inorder to maintain proper operation of the system. In many cases, theconcentration, feed rate and efficacy of the chemical treatment areimprecisely known and system characteristics (total volume, makeup andblowdown rates, holding time index, etc.) are estimated, variable orunknown. The systems can generally be divided into three major classes:closed, open, and once-through. In each case, transition metal can beeffectively used to determine and continuously monitor the concentrationand efficacy of chemical treatment and a system's operating conditionsand unknown characteristics.

In a "closed" system, the liquid and chemical treatment generally remainwithin the system and minimal amounts of liquid are added or discharged.Common examples of closed systems are continuous casting processes inthe metallurgical industry, refrigerating and air-conditioning units,radiator units, and recirculating cooling water systems in areas wherewater use or chemical discharges are severely limited. In those systems,the treatment can be lost through chemical/microbial degradation,deposition/corrosion processes, system leaks and low level discharges.

The common characteristics of "open" systems are that variable andsignificant amounts of liquid (makeup) and chemical treatment are addedand discharged (blowdown) from the working fluid. The system may or maynot be pressurized and subject to evaporative losses of fluid. Commonexamples of open systems are boilers, gas scrubbers and air washers,municipal sewage treatment, metal working and fabrication processes,paint spray booths, wood pulping and papermaking, and others. Chemicaltreatment can be lost through system discharges and leaks,deposition/corrosion processes, adsorption onto particulate matter,chemical/microbial degradation, etc.

"Once-through" systems generally involve a fluid and chemical treatmentwhich are added to a system, pass through the system a single time, andthen are discharged as effluent or transferred into another system. Muchlarger amounts of water are required in those systems than in comparable"closed" or "open" recirculating systems. Common examples ofonce-through systems are clarification and filtration units, mineralwashing and benefaction, boilers, and cooling for utilities andindustrial process streams.

In each of the above situations, the chemical treatment containing aknown quantity of transition metal is added to and distributed withinthe liquid system. The liquid can be sampled or continuously monitoredat any point of addition, from within the system or its discharge. Bycomparing absorbance of the system liquid with a standard solutioncontaining a known concentration of chemical treatment and transitionmetal, the concentration of the chemical treatment within the liquidsystem may be determined. In addition, by determining the transitionmetal concentration at different points in the system, the uniformity ofchemical treatment distribution and presence of low fluid flow andstagnant regions within the system can be quantified.

Stagnant or low fluid flow regions are inherent in some systems, inspite of continued addition and discharge of liquid(s). For example, oilfield applications (drilling, secondary and tertiary recovery methods,etc.) involve addition of chemical treatment(s) to a liquid which willpermeate slowly into some portions of a larger system. FIG. 3 shows thatalthough the true total volume (Z) of that system cannot be accuratelydetermined, the effective working volume (S) and average concentrationof the chemical treatment can be quantified by comparing the tracerconcentration in the liquid entering (I+T) and leaving the system (D+T).By comparing the individual concentrations of treatment components andtransition metal tracer, the efficiency and degradation of the treatmentand its components can be determined.

Based on the techniques described above, one may accurately determinemany operating parameters (total volume, holding time index, blowdownrate, unaccounted for system losses, chemical treatment efficacy, etc.)within the wide variety of systems.

The successful use of transition metal ion tracers described above havebeen accomplished in several systems. The following examples areillustrative of particular embodiments of the invention. It isemphasized that not all embodiments of this invention are illustratedwith the particularity given below. A typical calibration procedure isgiven below. To calibrate a spectrophotomer for measurement of Co IIconcentration, a series of solutions with known quantities of Co II wereprepared.

SPECTROMETER CALIBRATION PROCEDURE FOR CO II

The samples of cobalt solutions in Table 1 were obtained from a 100 ppmstock solution of Co(NO₃)6H₂ O and diluted with water to theconcentrations shown in Table 1. Fifteen ml samples of the stocksolution were mixed with a mask mix and a color reagent. The mask mixconsisted of an aqueous sodium citrate and sodium sulfite solution. Thecolor reagent (PAR) solution consisted of 1-3 drops 0.1 N sodiumhydroxide in approximately 50 mls of 0.2% pure pyridyl azo resorcinol inwater. To the first sample only, 10 drops of ethylene diamine tetraacetic acid (EDTA) solution was added to simulate 100% dilution at 530nm. The EDTA solution consisted of 5 gm Na₂ EDTA in 100 mls water with apH adjustment to 9 with NaOH.

                  TABLE 1                                                         ______________________________________                                        Calibration Data for Cobalt II                                                             Percent     Absorbance                                           [Co.sup.+2 ] ppm                                                                           Transmittance                                                                             (A)*                                                 ______________________________________                                        0**          100         0                                                    .01          98          .008                                                 .05          90          .045                                                 .1           81          .092                                                 .2           67          .174                                                 .3           57          .244                                                 .4           49          .310                                                 .5           45          .347                                                 .6           41          .387                                                 .7           38          .420                                                 1.5          31          .509                                                 ______________________________________                                         *(A) = -log (% T/100).                                                        **EDTA solution added to simulate 100% dilution.                         

Transmittance was measured with a Bausch and Lomb Spectrometer 2000 at awavelength of 530 nm. The data from Table 1 was used to generate acalibration curve. The tracer concentration of samples with unknowntracer concentration was determined by comparison with the curvegenerated from the data above.

EXAMPLE 1 Use of Cobalt Compound (Co⁺²) as Product Feed Tracer inRecirculating Water System

Tests were conducted in an integrated scaling unit (ISU) designed tosimulate an industrial cooling water system, such as the pilot coolingtower shown schematically in FIG. 1. The ISU contains a seven litersystem adapted to receive continuous streams of water, chemicaltreatment and various tracers. This minimizes variations inconcentrations of components during a test run. The streams are fedthrough syringe pumps that pump concentrated feed from a stock solutionprepared in sufficient quantity to last an entire test period. The ISUis a recirculating water system which contains a metal heat-exchangetube and is used to model cooling water systems.

Continuous blowdown is accounted for by continuous makeup and chemicaltreatment addition. These tests were conducted to provide data thatallows comparison of a cobalt tracer under various simulated treatmentconditions against tracers with known performance. Here mainly, a cobalttracer is evaluated by comparison of its performance with otheravailable methods of detecting chemical treatment.

The % of expected feed is obtained by dividing the observed amount oftracer by the expected amount of tracer in the system multiplied by100%. The expected amount of tracer is calculated by a mass balance ofconcentrated chemical feed added, makeup water added and blowdown waterlost.

Comparison of Cobalt Tracer (Co⁺²) with Aryl Sulfonic Acid FluorescentTracer and Active Phosphate Analysis

This example serves to compare Co⁺² as a tracer against fluorescenttracers and direct measurement of the active phosphate treating agent.

The ISU was started wherein two syringe pumps were activated. The firstpump injected a mixture comprising 57.3 weight percent deionized water,1.1 weight percent aryl sulfonic acid fluorescent tracer, 36.6 weightpercent acrylic acid base terpolymer and 1.0 weight percent Co⁺² asCo(NO₃)₂.6H₂ O (5 weight percent). The second pump injected an overlayof a mixture including deionized water, potassium hydroxide, phosphatecompounds, tetrapotassium pyrophosphate and phosphoric acid. The mixtureinjected from the first pump was diluted in the system water to 126.8ppm. The mixture injected from the second pump was diluted in the systemwater to 170.3 ppm. Grab samples were analyzed for total phosphorous,fluorescent tracer and C⁺². Table 2 shows the results. Transmittance wasdetermined spectrophotometrically with a Bausch and Lomb Spectrometer2000. The sample blank contained deionized water, EDTA, a mask mix andindicator. Samples include mask mix and indicator. The mask mix was asodium citrate and sodium sulfite aqueous solution. The color reagentwas a PAR solution as described above.

                  TABLE 2                                                         ______________________________________                                        Calculated Concentration of                                                   Chemical Feed Based on Tracers                                                           % of Expected Chemical Feed*                                                                   Based on                                          Time                        Fluores-                                                                             Based on                                   Elapsed  ppm     Based on   cent   Active                                     (Hr)     Co.sup.+2                                                                             Co.sup.+2  Tracer Phosphate                                  ______________________________________                                         0       .32     87.4%      96.8%  102.9%                                      19**    .094    24.4       53.5   20.0                                        45**    .091    24.4       39.4   11.8                                        50.75** .098    27.6       34.6   20.0                                        63.75** .121    36.2       28.7   13.5                                        66.25   .254    76.4       94.5   81.8                                        87.75   .206    63.8       104.7  63.5                                        95.25***                                                                              .175    55.9       111.8  58.8                                       113.75***                                                                              .119    36.2       116.5  38.8                                       117      .337    103.9      110.2  102.4                                      120      .278    85.0       112.6  83.5                                       136.5    .349    107.0      114.2  92.4                                       144      .355    109.4      115.0  89.4                                       159.75   .318    97.6       115.0  95.9                                       164.25   .339    103.9      128.3  95.3                                       166.5    .324    97.6       118.1  95.9                                       188.75   .402    122.0      126.8  95.9                                       210.25   .403    122.0      126.8  92.8                                       231.75   .384    115.7      126.8  96.5                                       239.5    .404    122.0      126.8  107.1                                      261.25   .426    131.5      133.1  104.7                                      279.75   .410    125.2      125.0  100.0                                      303.75   .429    131.5      128.3  102.4                                      311.25   .430    131.5      128.3  97.6                                       334.75   .474    143.3      126.8  104.7                                      ______________________________________                                         *Values >110% of expected chemical feed will result from increase in          concentration cycles of recirculating water due to slow evaporation of        water from system.                                                            **Test of tracer response based on loss of product feed.                      ***Outof-specification operation to test effects of high pH excursion.   

The purpose of the following analysis is to measure the differencebetween Co⁺² readings and fluorescent tracer readings and other activecomponent(s) of the treatment.

Chemical Feed Determination Analysis

When 63.75 hours elapsed, the syringe pumps were started. After thatpoint in time, there was an immediate rise in measured Co⁺² ionconcentration as well as fluorescent tracer concentration and activephosphate. Next, the effect of a high pH upset was evaluated as the pHof the system was increased to 8.3. The measured Co⁺² ion concentrationdropped to 0.119 ppm Co⁺² corresponding to 36.2% of the expected feed.At the same point in time, the fluorescent tracer concentration remainedrelatively high corresponding to 116.5 ppm concentration of treatment.When the pH was lowered to a normal operating value (pH 7.2) at anelapsed time of 117 hours, the measured Co⁺² ion concentration increasedto a corresponding 103.9% of the expected chemical feed. The drop in pHbelow 8 increased dramatically the solubility of the Co⁺² ion in thesystem. Very good results were obtained with Co⁺², once the pH wascontrolled at a level below 8.0 during an elapsed time of approximately136.5 hours to an elapsed time of approximately 279 hours. Also duringthat time, a 12,400 Btu/ft² /hr heater was turned on to increase thebasin temperature to 100° F. and provide a heat transfer surface wherebydeposit growth could occur. At an elapsed time of approximately 279hours until the end of the test, a 25,000 Btu/ft² /hr heater was turnedon to increase the basin temperature to 120° F. and very good resultswere still obtained with the Co⁺² tracer. The concentration of chemicaltreatment slowly increases with time due to constant evaporation of theprocess water throughout the test.

The concentration of Co⁺² ion was determined by the colorimetrictechnique described above. The fluorescent tracer concentration wasdetermined by comparison of the samples with a calibration curve oftracer concentration versus emission, [refer to J. R. Lakowicz;"Principles of Fluorescence Spectroscopy" (1983)]. The total phosphoruscontent was determined by persulfate oxidation of organophosphorusspecies to orthophosphate and subsequent formation of bluephosphomolybdate complex which was quantified spectrophotometrically,[refer to M. C. Rand; "Standard Methods for the Examination of Water andWastewater", 14th Ed. (1975)]. All concentrations of tracers andphosphorus containing species are expressed as % of expected chemicalfeed concentration.

This analysis shows that a Cobalt compound can function as a tracer andaccurately determine the chemical treatment feed rate at pH≦8. Theanalysis proves that Cobalt compounds can follow the proven fluorescenttracers and are superior in determining treatment feed rates than bydirect measurement of the treatment agent (e.g. total phosphorusconcentration). This analysis shows that the Co⁺² may be accuratelyquantified in the presence of active chemical treatment agents, othertracers and other compounds and complexes commonly found in industrialwater.

Deposit Analysis

The site of heaviest scaling was removed from a stainless steel heatexchanger within the ISU. The white deposit was readily dissolved inHCl. Table 3 shows the deposit enrichment ratio (DER) of the variouscomponents within the scale.

                  TABLE 3                                                         ______________________________________                                        DER of Scale Formation                                                        Within ISU for Various Compounds                                              Component               DER                                                   ______________________________________                                        Fluorescent Tracer      .01                                                   Co.sup.+2 Ion           .92                                                   Ortho Phosphate         1.04                                                  Total Phosphorus        1.85                                                  Pyro Phosphate          2.54                                                  Hydroxyethanediphosphonicacid (HEDP)                                                                  4.25                                                  ______________________________________                                    

The enrichment ratio data shows that the Co⁺² ion has less of a tendencyto deposit in the above described system than active treatmentformulation components and by-products such as ortho phosphate, pyrophosphate, total phosphorus and HEDP. Therefore, chemical feeddetermination using a Co⁺² ion is acceptable within the presence of theabove-identified active treatment formulation. Note, also, that the Co⁺²ion enrichment ratio is deceptively high in this analysis because thesystem pH was brought above pH 8 allowing some precipitation of Co⁺² ionto occur.

EXAMPLE 2

A test was conducted in an integrated scaling unit (ISU) designed tosimulate an industrial cooling water system with chemical treatment inthe feed as described in Example 1.

Comparison of Cobalt Ion Tracer (Co⁺²) with Aryl Sulfonic AcidFluorescent Tracer, Lithium Ion Tracer and Active Phosphate Analysis

The ISU was started wherein two syringe pumps were activated. The firstpump injected an aqueous solution comprising 71.50 weight percentdeionized water, 0.37 weight percent aqueous sodium hydroxide (50 weightpercent aqueous), 14.44 weight percent aqueous potassium hydroxide (45weight percent aqueous), 5.41 weight percent aqueous tetra potassiumpyrophosphate (40 weight percent aqueous), 4.86 weight percentphosphoric acid (25 weight percent aqueous), 2.12 weight percent aqueoussodium tolyl triazole (50 weight percent aqueous), 1.21 weight percentaqueous HEDP (40 weight percent aqueous) and 0.10 weight percent arylsulfonic acid fluorescent tracer. The second pump injected a mixturecomprising 94.35 weight percent deionized water; 4.57 weight percent ofa terpolymer consisting of an acrylic acid base, acrylamide andacrylamidomethane-sulfonic acid; 0.63 weight percent Co(NO₃)₂.6H₂ O (1.0weight percent Co⁺²) and 0.45 weight percent LiCl (0.6 weight percentLi⁺). The mixture injected from the first pump was diluted in the systemwith water to 132.3 ppm. The mixture injected from the second pump wasdiluted in the same system with the same water to 171.3 ppm. Grabsamples were analyzed for total phosphorus, fluorescent tracer, lithiumtracer and Co⁺² tracer. Table 4 shows the results. Transmittance wasdetermined with a Bausch and Lomb Spectrometer 2000.

                  TABLE 4                                                         ______________________________________                                        Calculated Concentration of                                                   Chemical Feed Based on Tracers                                                % of Expected Chemical Feed                                                                    Based on                                                     Time    Based on Fluores-   Based on                                                                             Based on                                   Elapsed Co.sup.+2                                                                              cent       Lithium                                                                              Active                                     (Hr)    Ion      Tracer     Ion    Phosphate                                  ______________________________________                                        0       47        70         72    59                                         17.58   71        75         85    50                                         41.58   75        92        100    64                                         71.58   104       97        115    76                                         104.33  113      105        118    83                                         129.08  115      106        125    86                                         137.58  102      106        125    79                                         185.58* 22       127        125    37                                         262.16* 36       117        120    28                                         ______________________________________                                         *Out-of-specification operation to test effects of high pH excursion.    

The purpose of the following analysis is to compare Co⁺² tracer readingsand fluorescent tracer readings and lithium ion tracer readings andother active components of the treatment.

Chemical Feed Determination Analysis

For the first approximately 185 hours during pump operation the pH wasmaintained at 7.0±0.3. Scaling and corrosion were observed on the heatexchanger tube. Lithium ion tracer, fluorescent tracer and Co⁺² trackedclosely while the active phosphate lagged behind. Under theseconditions, the tracers were not significantly being incorporated intothe scale deposits. Total Fe in the cooling water ranged from 0.5-0.6ppm. At an elapsed time of 185.58 hours, the pH had increased to 8.0where it was noted previously that Co⁺² undergoes precipitation. Asexpected, Co⁺² levels dropped off. Only lithium and aryl sulfonic acidtracked near 100% expected feed.

The concentration of each component was determined as described inExample 1. The concentration of lithium ion was determined byconventional atomic absorption spectroscopy. All concentrations oftracers and phosphorus containing species are expressed as % of expectedchemical feed.

This analysis shows that a Co⁺² ion can be used to accurately determinethe chemical treatment feed rate. The analysis proves that Co⁺² ionsfollow the proven fluorescent tracers and perform very effectively ascompared to other currently used methods for determining treatment feedrates. This analysis shows that the Co⁺² ions may be accuratelyquantified in the presence of active chemical treatment agents, othertracers and other compounds and complexes commonly found in industrialwater.

EXAMPLES 1-2 Conclusion

Since Co⁺² ion increases in solubility below pH=8, it may be desirableto use Cobalt tracers in water treatment systems with pH levels below 8.Ions, elements, and compounds commonly encountered in industrial coolingwater systems (i.e. Ca⁺², Mg⁺², HCO₃ /CO₃ ²⁻, PO₄ ⁻³, P₂ O₇ ⁻², polymerand hydroxy ethane diphosphonic acid) do not affect performance of Co⁺²ions as total product feed tracer. Nevertheless, ions that respond tothe color reagent (i.e. copper ions and iron ions) must be masked toprevent erroneous readings.

EXAMPLE 3 Use of VO₃ ⁻ as Product Feed Tracer in Pilot Cooling Tower(PCT)

A test was conducted on a pilot cooling tower (PCT) designed to simulatean industrial cooling water system. The PCT contains a 50 liter capacityadapted to simulate recirculating water, chemical treatment feed,deposit formation and corrosion on heat exchangers, blowdown and makeup,and evaporative cooling from a tower fill. The test was conducted toprovide data that allows comparison of a vanadate ion (VO₃ ⁻) as atracer under various simulated treatment conditions against aconventional chemical feed determination method.

Alternative Sample Analysis

As described in the calibration procedure, pyridylazo resorcinol (PAR)color reagent may be used successfully as an indicator with cobalt IIions when background ions are masked with a sodium citrate and sodiumsulfite solution. When sampling VO₃ ⁻, the sample is buffered at pH 5.5.The buffer converts VO₃ ⁻ to VO₂ ⁺, which reacts completely with the PARsolution. However, VO₂ ⁺ also reacts with conventional masking agents.Therefore, VO₂ ⁺ is hidden from detection when masking agents arepresent.

To eliminate the need for masking agents, H₂ O₂ may be added to a samplesolution before the PAR color reagent to form 2:1 diperoxyvanadate,VO(O)₂ ⁻, which does not react with the PAR solution. To another sample,the VO₂ ⁻ ions are allowed to completely react with the PAR solution.The difference in the transmittance between the two samples provides anindication of the concentration of vanadium ions present within thesample.

Comparison of Vanadate Ion Tracers (VO₃ ⁻) with Active PhosphateAnalysis

A single water treatment formulation containing 54.55 weight percentdeionized water, 16.1 weight percent aqueous sodium hydroxide (50 weightpercent aqueous), 7.0 weight percent amino-tris (methylene phosphoricacid) (Dequest 2000 manufactured by Monsanto), 12.0 weight percentorgano phosphonocarboxylic acid (50 weight percent aqueous), 4.7 weightpercent sodium tolyltriazole (50 weight percent aqueous), 2.5 weightpercent fatty dicarboxylic acid (Diacid 1550 distributed by WestVaco),2.0 weight percent surfactant and 1.15 weight percent ammoniummetavanadate with the VO₃ ⁻ tracer level controlled at 0.5 ppm V at a100 ppm product level. PCT test results are summarized in Table 5.

                  TABLE 5                                                         ______________________________________                                        Chemical Feed Determination Based on                                          VO.sub.3.sup.-  Concentration, Active Phosphate                               Concentration and Blowdown Measurement                                                Calculated Concentration                                                      of Chemical Feed (ppm)                                                                               Based on                                                            Based on  Blowdown/                                      Time      Based on   Active    Syringe                                        Elapsed   VO.sub.3.sup.-                                                                           Phosphate Measurement*                                   ______________________________________                                        200 ppm of                                                                              197        200       --                                             product                                                                       0 (startup)                                                                             190        201       --                                             2.75      195        204       --                                             15.67     187        187       --                                             32.60     172        138       --                                             43.50     164        109       --                                             63.67     132        77        --                                             68.00     132        81        --                                             71.00     131        84        --                                             97.50     125        86        --                                             104.30    123        82        --                                             126.50**  118        88        --                                             153.33    113        85        113                                            178.20    111        86        114                                            204.50    108        80        114                                            227.67    104        76        106                                            254.40    106        81        111                                            298.25    107        83        111                                            324.67    108        85        115                                            ______________________________________                                         ##STR1##                                                                      **Typically, product is initially added (200 ppm) at twice the specified      maintenance product feed rate (100 ppm). The concentration of treatment i     the system will coincide with treatment feed rate (based on                   blowdown/syringe measurements) after about 150 hours.                    

The VO₃ ⁻ ions were quantified by comparison of transmitted light withsamples of known concentration as described above in the alternativesample analysis. Additionally, product feed rate was calculated fromsyringe pump and blowdown measurements. The active phosphate content wasdetermined by persulfate oxidation of organophosphorus species toorthophosphate and subsequent formation of blue phosphomolybdate complexwhich was quantified photometrically; [refer to M. C. Rand; "StandardMethods for the Examination of Water and Wastewater", 14th Ed. (1975)].

Comparison of the treatment feed rate in the system predicted by the VO₃⁻ ions versus the measurement of active phosphate demonstrates thesuperior accuracy of the measurement of VO₃ ⁻ ions over the phosphatemethod. At an elapsed time of 324.67 hours, the active phosphate methodindicated 30 ppm less than the accurate syringe pump and blowdowncalculation. The difference in the levels arise from deposition of theorganophosphorus components of the treatment onto the heat-exchangertubes. At the same time, quantitative measurement of the VO₃ ⁻ ionsindicated only 7 ppm less than the calculated product level based onblowdown/syringe feed measurements. The differences between the VO₃ ⁻ion level(s) and the total phosphorus level is a good indication oftreatment effectiveness, since it quantifies how much of the activephosphorus-containing components are being lost within the system fromdeposition and corrosion processes. In an "ideal" operating system, thetotal phosphorus and VO₃ ⁻ ion levels would all indicate an identicaltreatment concentration.

Comparison of Vanadate Ion Tracers (VO₃ ⁻) with Chromate Ion Tracers(Cr₂ O₇ ⁻²)

A single water treatment formulation containing 53.15 weight percentdeionized water, 16.1 weight percent sodium hydroxide (50 weight percentaqueous), 7.0 weight percent amino-tris (methylene phosphoric acid)(Dequest 2000 manufactured by Monsanto), 12.0 weight percent organophosphonocarboxylic acid (50 weight percent aqueous), 4.7 weight percentsodium tolyltriazole (50 weight percent aqueous), 2.5 weight percentfatty dicarboxylic acid (Diacid 1550 distributed by WestVaco), 2.0weight percent surfactant, 1.4 weight percent sodium dichromatedihydrate and 1.15 weight percent ammonium metavanadate with the VO₃ ⁻tracer level controlled at 0.5 ppm V at a 100 ppm product level. PCTtest results are summarized in Table 6.

                  TABLE 6                                                         ______________________________________                                        Chemical Feed Concentration Determination                                     Based on VO.sub.3.sup.-  Concentration and Cr.sub.2 O.sub.7.sup.-2            Concentration                                                                                       Calculated Concentration                                Time                  of Chemical Feed (ppm)*                                 Elapsed               Based on Based on                                       (Hr)     pH           VO.sub.3.sup.-                                                                         Cr.sub.2 O.sub.7.sup.-2                        ______________________________________                                        0        7.4          196      192                                            8.48     --           193      175                                            23.77    8.44         171      155                                            33.15    8.47         160      147                                            41.42    --           160      150                                            49.72    8.73         152      146                                            58.92    8.73         143      136                                            80.00    8.50         130      126                                            110.50   8.51         116      112                                            141.83   8.67         111      105                                            172.83   9.20         110      102                                            202.67   8.43         108      103                                            210.92   9.00         108      107                                            212.17   4.90**       131       24                                            213.17   4.90**       119       2                                             214.17   4.90**       115       2                                             215.17   5.40**       112       2                                             216.17   7.7**        --        10                                            216.87   7.86**       --        11                                            217.17   7.9**        112       11                                            218.17   8.1**         99       11                                            222.27   8.37          76       11                                            234.75   8.3           56       16                                            270.60   8.45          46       16                                            321.83   8.50          72       50                                            383.72    --           77       60                                            ______________________________________                                         *Typically, product is initially added (200 ppm) at twice the specified       maintenance product feed rate (100 ppm). The concentration of treatment i     the system will coincide with treatment feed rate (based on                   blowdown/syringe measurements) after about 150 hours.                         **Out-of-specification operation to test effects of low pH excusion.     

The unknown quantities of VO₃ ⁻ ions and Cr₂ O₇ ⁻² ions were quantifiedby comparison of transmitted light with samples of known concentration.Transmittance was determined with a Bausch and Lomb Spectrometer 2000.

Comparison of the treatment feed rate in the system predicted by the VO₃⁻ ions versus the measurement of Cr₂ O₇ ⁻² tracer demonstrates thesuperior accuracy of the measurement VO₃ ⁻ ions over that of Cr₂ O₇ ⁻²ions when pH excursions occur. The data as shown in Table 5 reflects anacid upset initiated at an elapsed time of 210.92 hours. The low pHcauses a sharp rise in mild steel corrosion rate of the heat exchangerwhich is known to cause losses of the bichromate tracer. The vanadate isnoticeably more resistant to that loss than bichromate as shown in FIG.4. Also shown in FIG. 4, the vanadate tracer recovers more quickly thanthe bichromate.

EXAMPLE 3 Conclusion

The benefits of using vanadium compounds are as follows:

Vanadium oxyanions (VO₃ ⁻) does not tend to precipitate with othersolids which are formed between pH 7-9.

Vanadium oxyanions (VO₃ ⁻) are resistant to precipitation in thepresence of corroding mild steel heat exchange tubes.

EXAMPLE 4

Several transition metal ions were evaluated in aqueous systems at pH9.3 and pH 7.0. The performance of each ion and oxyion was determined bythe following equation:

    % Recovery=(FS/US)×100%;

wherein

FS=Concentration of metal ion (ppm) in filtered sample after passingthrough 0.45 μm filter

US=Initial concentration of transition metal ion (ppm) in unfilteredsample A maximum value of %Recovery=100% shows that the transition ionwas completely soluble in the system at the given pH. Results are shownin Table 7 and Table 8 below.

                  TABLE 7                                                         ______________________________________                                        Performance Comparisons of                                                    Transition Metal Tracers (at pH 7)                                                               Transition Element                                                 Element    Group Number                                               Metal Ion                                                                             Form Used  Periodic Table                                                                              % Recovery                                   ______________________________________                                        Silver  Ag.sup.+   IB            22%                                          Zinc    Zn.sup.+2  IIB           97%                                          Yttrium Y.sup.+3   IIIB          91%                                          Zirconium                                                                             Zr.sup.+4  IVB            8%                                          Vanadium                                                                              V.sup.+5 * VB            100%                                         Chromium                                                                              Cr.sup.+3 **                                                                             VIB           99%                                          Manganese                                                                             Mn.sup.+2  VIIB          98%                                          Nickel  Ni.sup.+2  VIIIB         100%                                                            (col. 3)                                                   Cobalt  Co.sup.+2  VIIIB         95%                                                             (col. 2)                                                   Aluminum                                                                              Al.sup.+3  IIIB          70%                                          ______________________________________                                         *as Vanadate (VO.sub.3.sup.-).                                                **Note distinction from chromate (Cr.sub.2 O.sub.7.sup.-2), where             Cr.sup.+6 is formal oxidation state of metal center.                     

                  TABLE 8                                                         ______________________________________                                        Performance Comparisons of                                                    Transition Metal as Tracers (at pH 9.3)                                                          Transition Element                                                 Element    Group Number                                               Metal Ion                                                                             Form Used  Periodic Table                                                                              % Recovery                                   ______________________________________                                        Silver  Ag.sup.+   IB            28%                                          Zinc    Zn.sup.+2  IIB           36%                                          Yttrium Y.sup.+3   IIIB          63%                                          Zirconium                                                                             Zr.sup.+4  IVB            6%                                          Vanadium                                                                              V.sup.+5 * VB            100%                                         Chromium                                                                              Cr.sup.+3 **                                                                             VIB           94%                                          Manganese                                                                             Mn.sup.+2  VIIB          73%                                          Nickel  Ni.sup.+2  VIIIB         67%                                                             (col. 3)                                                   Cobalt  Co.sup.+2  VIIIB         50%                                                             (col. 2)                                                   Aluminum                                                                              Al.sup.+3  IIIB          60%                                          ______________________________________                                         *as Vanadate (VO.sub.3.sup.-).                                                **Note distinction from chromate (Cr.sub.2 O.sub.7.sup.-2), where             Cr.sup.+6 is formal oxidation state of metal center.                     

As shown in Table 7 and Table 8, Vanadium (VO₃ ⁻) and Chromium (Cr⁺³)exhibit excellent solubility in both systems, whereas other transitionmetals such as zinc (Zn⁺²), yttrium (Y⁺³), nickel (Ni⁺²) and cobalt(Co⁺²) are better suited in systems with a pH 7.0 than pH 9.3.Solubility at lower pH for these transition metals show an advantageover non-transition metals such as aluminum (Al⁺³) which are not assoluble at pH 7 as shown in Table 7. Furthermore, Table 7 and Table 8show that silver (Ag⁺) and zirconium (Zr⁺⁴) are not suitable at eitherpH 7 or pH 9.3.

Conclusion

While the invention has been described in connection with specificembodiments thereof, it will be understood that it is capable of furthermodifications. This application is intended to cover any variations,uses or adaptions of the invention following, in general, the principlesof this invention, and including such departures from the presentdisclosure as come within known and customary practice within the art towhich the invention pertains.

What is claimed is:
 1. A product for monitoring a liquid systemcomprising at least one metal tracer which is a transition metal in theform of an ion, cation, oxyanion or other charged radical which issoluble in the liquid system, wherein said tracer is present in theproduct in an amount such that, within the liquid system to which theproduct is to be added, a concentration of said tracer of from 10 partsper billion to 2 parts per million is realized.
 2. A product formonitoring a liquid system as in claim 1 wherein said transition metaltracer is more resistant to degradation or precipitation than ChromiumVI tracers.
 3. A product for monitoring a liquid system as in claim 2wherein the liquid system is aqueous.
 4. A product for monitoring aliquid system as in claim 2 wherein the transitional metal tracer isinert in said liquid system.
 5. A product for monitoring a liquid systemas in claim 2 wherein said liquid system is selected from staticsystems, open-end systems, closed-end systems and once-through systems.6. A product for monitoring a liquid system as in claim 1 wherein saidtransition metal is present in an amount less than or equal to 0.5 ppm.7. A product for monitoring a liquid system as in claim 2 wherein saidliquid system is a cooling water system.
 8. A product for monitoring aliquid system as in claim 7 wherein said cooling water systemexperiences evaporative losses of water and temperature fluctuation. 9.A product for monitoring a liquid system as in claim 1 wherein saidtransition metal tracer is selected from the group of transition metalsconsisting of vanadium, cobalt, nickel, titanium, tin, molybdenum,yttrium, tungsten and mixtures thereof.
 10. A product for monitoring aliquid system as in claim 1 wherein said transition metal tracer ismolybdenum.
 11. A product for monitoring a liquid system as in claim 1wherein said transition metal has a background level in the liquidsystem of no more than 10%.
 12. A product for monitoring a liquid systemas in claim 1 additionally comprising one or more treatment agentsselected from the group consisting of scale inhibitors, phosphates,organophosphates, corrosion inhibitors and mixtures thereof.
 13. Aproduct for monitoring a liquid system comprising at least one metaltracer which is a transition metal in the form of an ion, cation,oxyanion or other charged radical which is soluble in the liquid systemwherein said transition metal tracer is selected form the group oftransition metals consisting of vanadium, cobalt, nickel, titanium, tin,molybdenum, yttrium and tungsten and mixtures thereof, wherein saidtracer is present in the product in an amount such that, within theliquid system to which the product is to be added, a concentration ofsaid tracer of from 10 parts per billion to 2 parts per million isrealized, wherein said transition metal tracer is essentially inert insaid liquid system and wherein said transition metal tracer is presentin a form in which it may be detected by visual colorimetric methods,spectrophotometric methods, the transmission of light or the absorptionof ultraviolet or visible light in samples taken from said liquidsystem.
 14. A product for monitoring a liquid system as in claim 13wherein said product further comprises one or more treatment agents forsaid liquid system selected from the group consisting of scaleinhibitors, phosphates, organo-phosphates, corrosion inhibitors, andmixtures thereof.
 15. A product for monitoring a liquid system as inclaim 13 wherein said liquid system is an aqueous system.
 16. A productfor monitoring a liquid system as in claim 13 wherein said liquid systemis a cooling water system.
 17. A product for monitoring a liquid systemas in claim 1 wherein said transition metal tracer is more resistant todegradation or precipitation than Chromium VI tracers.
 18. A product formonitoring a liquid system consisting essentially of at least onetransition metal tracer in the form of an ion, cation, oxyanion or othercharged radial which is present in the product in an amount such that,within the liquid system to which the product is to be added, aconcentration of said tracer of from 10 parts per billion to 2 parts permillion is realized.
 19. A product for monitoring a liquid system as inclaim 18 wherein said transition metal tracer is more resistant todegradation or precipitation than Chromium VI tracers.
 20. A product formonitoring a liquid system as in claim 18 wherein the transition metaltracer is inert in said liquid system.
 21. A product for monitoring aliquid system as in claim 18 wherein the transition metal tracer isinert in said liquid system.
 22. A product for monitoring a liquidsystem as in claim 18 wherein said liquid system is selected from staticsystems, open-end systems, closed-end systems and once-through systems.23. A product for monitoring a liquid system as in claim 18 wherein saidliquid system is a cooling water system.
 24. A product for monitoring aliquid system as in claim 18 wherein said cooling water systemexperiences evaporation losses of water and temperature fluctuation. 25.A product for monitoring a liquid system as in claim 18 wherein saidtransition metal tracer is selected from the group of transition metalsconsisting of vanadium, cobalt, nickel, titanium, tin, molybdenum,yttrium, tungsten and mixtures thereof.
 26. A product for monitoring aliquid system as in claim 18 wherein said transition metal tracer ismolybdenum.
 27. A product for monitoring a liquid system as in claim 18wherein said transition metal has a background level in the liquidsystem of no more than 10%.
 28. A product for monitoring a liquid systemas in claim 18 wherein said transition metal tracer is present in anamount less than or equal to 0.5 ppm.